Rigid polyurethane foams find many diverse applications in industry and especially in construction and insulation where fire-resistance is desirable and may even be absolutely necessary.
One process for imparting fire-resistance properties to polyurethane foam consists of incorporating into the foam flameproofing additives, such as antimony oxide or halogenated and/or phosphorus-containing compounds, e.g. tris-(dibromopropyl) or tris-(dichloropropyl) phosphates, chlorinated biphenyls and halogenated hydrocarbons. These additives which are not bonded chemically to the base polymer, are incapable of providing uniformly-distributed permanent fire-resistance. Furthermore, as a general rule, they have a plasticizing effect on the foam and, consequently, have an adverse effect on its mechanical properties, and especially on its compressive strength and on its dimensional stability.
Another method for manufacturing fire-resistant polyurethane foam consists of similarly employing halogenated and/or phosphoruscontaining polyols.
French Patent 1,350,425 of Mar. 12, 1963, in the name of Olin Mathieson Corp., describes the use of halogenated polyetherpolyols (manufactured by adding epihalohydrins to monomeric polyhydric alcohols containing at least two hydroxyl groups). Although the cellular polyurethanes resulting from the reaction of organic polyisocyanates with these halogenated polyetherpolyols possess permanent and satisfactory fire-resistance properties, their dimensional stability is only mediocre. Furthermore, these polyether-polyols are unstable when stored in the presence of amine-type compounds usually employed in the formulation of pre-mixes for polyurethane foams.
Belgian Patent 798,674 of Apr. 25, 1973, describes polyether-polyols which are also derived from epichlorohydrin and which have a halogen content which is comparable to that of the halogenated polyether-polyols disclosed by Olin Mathieson Corp.; these polyether-polyols are characterized by the presence of terminal .alpha.-diol groups. The rigid and semi-rigid cellular polyurethanes which are manufactured by employing such halogenated polyether-polyols possess excellent mechanical properties, especially good dimensional stability, in addition to good fire-resistance. The relatively high viscosity of these polyether-polyols nevertheless somewhat complicates their processing.